Environmental Engineering Reference
In-Depth Information
phosphorus are rare, with the vast majority (more than 75% of cases) yielding reductions in load. For
nitrate the vast majority of wetland and wet retention basin applications also yielded reductions in load,
probably as a result of uptake of nitrate by aquatic plants. For nitrate 40% or more of the biofilter and
filter applications resulted in increases in nitrate loads perhaps reflecting conversion of organic nitrogen
and ammonia to nitrate in the course of passing through the filter.
With respect to other urban BMPs, Novotny (2003, p. 91) notes that residential areas with natural swale
drainage produced pollution loads that are approximately one order of magnitude lower than pollution
loads from similar land with storm sewer drainage. Terstriep et al. (1982) found that mechanical street
sweeping at frequencies as great as twice weekly is not effective in reducing the total loads of pollutants
in urban storm runoff. Indications of increases in the loads of pollutants during sweeping were at least as
strong as were indications of reductions. The fact that street sweeping mainly captures coarse materials
while pollutants are attached to finer materials is the suspected cause of these results.
The key conclusion from the data summarized by Parson et al. (2004) is that well designed and
maintained urban BMPs can reduce nutrient loads in runoff as is the case for agricultural BMPs.
However, if urban BMPs are not properly installed and maintained it is possible that nutrient loads can be
magnified.
Table 9.10 Summary of Nutrient Removal Efficiency Medians and Ranges by Nutrient and BMP Type. (after Parson
e t al., 2004)
BMP Type
Biofilter-
Grass
Strip
Detention
Basin
(dry)
Hydro-
dynamic
Devices
Pollutant
Biofilter-
Grass Strip
Retention
Basin (wet)
Filter
Wetland
TP Median (%)
(Range)
No. of studies
34.0
(-107 to 80)
n = 11
26.0
(-25 to 99)
n = 20
34.0
(-156 to 100)
n = 27
51.0
(-78 to 88)
n = 19
15.5
(-9 to 66)
n = 8
80.5
(14 to 97)
n = 56
43.5
(-267 to 100)
n = 40
OP Median (%)
(Range)
No. of studies
61.0
(-163 to 91)
n = 19
8.0
(-527 to 79)
n = 14
TN Median (%)
(Range)
No. of studies
24.0
(-196 to 73)
n = 13
31.5
(15 to 71)
n = 10
32.0
(-12 to 76)
n = 22
25.0
(-152 to 76)
n = 19
71.5
(4 to 99)
n = 16
Note: TP = total phosphorus, OP = orthophosphate, TN = total nitrogen, NO3 = nitrate, blanks indicate insufficient data
-5.5
(-352 to 72)
n = 10
9.0
(-40 to 99)
n = 11
-9.0
(-87 to 64)
n = 10
61.5
(-85 to 97)
n = 20
NO3 Median (%)
(Range)
No. of studies
9.4 Waterborne and Water-Contact Diseases
Waterborne diseases are caused by pathogenic microorganisms that are directly transmitted when
contaminated fresh water is consumed. Dermal (skin), eye, and ear contact with pathogens in contaminated
water also can lead to diseases and illnesses known as water-contact diseases. Waterborne diseases are one
of the primary causes of death in children in developing countries and also cause substantial misery around
the world. Diarrheal disease (including cholera) alone is responsible for the deaths of 1.8 million people
every year, 90% are children under 5 (WHO, 2004). A significant amount of disease could be prevented
especially in developing countries through better access to safe water supply, adequate sanitation facilities,
and better hygiene practices.
This section focuses on pathogens in rivers and their monitoring, control, and management, and, thus,
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